Insides of long conduits such as pipelines can be difficult to clean, and yet many fluids that are advantageously transported by pipelines have a tendency to deposit solids that eventually would plug the conduit. For example, crude oils contain paraffins that may precipitate as wax and adhere to the pipe wall if the crude oil cools as it flows down a pipeline.
Mechanical cleaning devices, commonly called pigs, are often used to clean such pipelines. Pigs are generally plugs that can slide through the pipeline by the force of fluids behind the pig, removing undesirable materials by pushing these materials in front of the pig. In long pipelines, stations to launch and catch these pigs are typically provided in the pipeline. Typical pigs are not particularly effective in removing scum deposits such as wax from crude oil pipelines because solids that are removed tend to accumulate in front of the pig. These long accumulations are heavy and viscous and eventually prevent the pig from progressing further down the pipeline thus plugging the pipe. With wax deposits within a pipeline, other methods to remove the wax solids are sometimes employed. For example, the pipeline can be flushed with a solvent that dissolves the wax. This is typically very expensive because time is required for the solvent to "soak" loose the wax, the solvent is generally expensive, large volumes of solvent are often required, and the contaminated solvent is generally of considerably less value than the clean solvent.
A pipe cleaning device is suggested by Judy J. Werlink and David E. Rowell of the Kennedy Space Center that overcomes some of the disadvantages of other pipe cleaning pigs. This pipe cleaning device includes a rotating brush that is rotated by fluids passing through the pipe at a velocity greater than the velocity of the pipe cleaning device. The brush is attached to a turbine wheel, the turbine wheel effective to translate energy from the flowing fluid to rotation energy. The device must be anchored by a cable to provide that the device moves through the pipeline at a velocity sufficiently different from the fluids to result in rotation of the brush. The necessity of the cable restricts the length of pipeline that can be cleaned because of the weight of an extended length of cable. For example, a pipeline having a length of greater than about a mile would be very difficult to clean with this device. Further, a tensioner and a seal must be provided around the cable where the cable enters the pipeline. This seal provides an opportunity for pipeline contents to escape resulting in unwanted emissions.
It is desirable to have a method and apparatus that can be used to remove solids from the inside of conduits wherein extended lengths of conduit can be cleaned and wherein solids will be flushed and thus removed down the pipeline as they are removed from the wall of the conduit.
It is therefore an object of the present invention to provide a method and apparatus to remove adhered solids from the inside of a conduit wherein a cleaning device does not require a cable anchor, and wherein flow through the pig is provided to remove loose solids ahead of the movement of the pig. It is a further object to provide such an apparatus and method wherein extended lengths of conduit can be cleaned.